The present invention relates a combination of techniques to produce a high purity metal salt product utilizing the selectivity of an adsorbent to remove species from a liquid containing mixtures of ions and then subjecting the loaded resin to a chromatographic displacement utilizing the most selectively adsorbed species to displace undesired co-adsorbing impurities, and regardless of whether or not the most selectively adsorbed species is present as a minor constituent in the feed solution.
Chromatographic purifications have been used on an analytical scale for many decades. Continuous chromatography has been able to be practiced on a production scale only in several selected industries (e.g., corn syrup industry sugar separations) as well in applications for rare earth separations & purifications.
Techniques for uranium recovery using Weak Acid Cation (WAC) resins is the subject of Robert Kunin's works, including “Recovery of Uranium from Carbonate Leach Liquors Using Weak Acid Cation Resins, Carmen & Robert Kunin, Reactive Polymers, 4 (1986) 77-89 and in a U.S. Pat. No. 4,606,894—“Recovery of Uranium from Carbonate Leach Liquors Using Carboxylic Acid Cation Exchange Resin”, which patent is incorporated by reference herein. The ability of these to produce a high quality concentrated product is limited. The Kunin patent reference teaches a cation exchanger to remove uranium cation from solution with the uranium cation simply being later removed from the cation exchanger and further purified to a condition which would enable its return to groundwater.
The Kunin method produces an acidic dilute product from which uranium is either precipitated as a diuranate by adding a base or purified further by anionic exchange. Calcium is removed as well as cationic uranium, and the product uranium concentration will depend upon the amount of Calcium present as well as upon the volume of eluate. Further processing steps are necessary to separate the uranium from the uranium/calcium mix eluted from the resin, as well as from the carbonate and other contaminants such as molybedenum and vanadium. What is needed is a process which takes advantage of components already within an ion exchange system to produce a higher purity product of higher concentration as well as to produce non-product streams which require less processing and are simply recycled within the existing process scheme.
In similar vein, the work by Blokihin et alia, “Sorption of Rehium (VII) on Gel and Macroporous Anion Exchangers of Different Basicities from Solutions of Mineral Acids and Their Ammonium Salts”, Russian Journal of Applied Chemistry, Vol. 78. No. 9, 2005 pp. 1411-1415, deals with the selectivity of Weak Base exchangers, Purolite A170 and A172 and a composite exchanger Purolite SIM202 and shows the strong selectivity for rhenium under acidic conditions. What is not evident from the literature is the novel technique, outlined in this invention, for further enhancing the natural selectivity inherent in an adsorbent through combining with this selectivity a chromatographic frontal displacement process to effectively produce a valuable final product consisting of a highly pure solution of a salt of the most selectively held species.